Jacketing uranium



United States Patent() JACKETING URANIUM Henry A. Saller and John R. Keeler, Columbus, Ohio,

assignors to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Application July 20, 1949 Serial No. 105,907

11 Claims. (Cl. 204-1932) 2 This invention deals with the plating of uranium, and in particular with the bonding, to uranium, of plates of -iron, or cobalt, or nickel, or metals based thereon or alloys thereof.

For most uses uranium has to be protected against corrosion, and thus it is enclosed in a metal container or canned; for instanceU for the generation of power by fission, is used in the form of blankets, rods, slugs, or tubes which are enclosed in a jacket of these above-mentioned metals and preferably of nickel or stainless steel. For all purposes it is necessary that the jacket is bonded to the uranium and that the bond is reliable, durable and resistant to the elevated temperatures prevalent during operation of the power pile.

It is thus an object of this invention to provide a bond between uranium and metals of the iron group of the periodic system of'elements which has a long service life even at elevated temperatures.

It is another object of this invention to provide a bond between uranium and metals of the iron group which has a high thermal conductivity.

It is still another object of this invention to provide a bond between uranium. and metals of the iron group which is free from cracks and voids and remains in that condition during use at elevated temperatures.

It is also an object of this invention to provide a bond between uranium and metals of the iron group which is characterized by a high degree of homogeneity.

These and other objects are accomplished by coating both surfaces to be joined, namely, the uranium surface and the surface of the jacket or the coating, with silver, amalgamating or alloying these silver coatings with mercury or indium, assembling the uranium core and the metal jacket, exerting pressure, e.g., at room temperature, on this assembly and thereby reducing the area of the assembly, and finally heating the assembly in order to homogenize the silver alloys by diifusion.

The silver layer has been applied to the uranium and the jacket by hot dipping as well as by electro-deposition. While both methods yield satisfactory coatings, the latter method is preferred because no oxide formation or oxygen absorption takes place in that case.

The thickness of the silver layers may be varied considerably and is advantageously adjusted to the dimensions and the use of the final article. For plating the inside of the jacket, for instance in the case of a nickel jacket, a thickness ranging from 0.0001 to 0.001" has been found satisfactory, while for the silver layer on the uranium article a thickness of 0.002 to 0.005 was preferred. In deciding on the thickness of these coatings, it is well to allow for a clearance of from 0.015 to 0.01" between the jacket and the uranium core.

Prior to the amalgamating or alloying step, it is advantageous, though not obligatory, to clean the surfaces. Carbon tetrachloride has been found suitable for this purpose. Thereafter the silver coatings are alloyed withmercury or indium in any conventional manner, and the uranium and jacket are then assembled. The unit is then pushed through a die, for instance, in the case of cylindrically shaped articles, through a wire-drawing die whereby the area is reduced; an area reduction of from 5 to 10% with regard to the actual metal present suffices. The load applied during extrusion is dependent on the dimension of the article and other factors which are known. to those skilled in the art. In most cases a pressure of about 325 p.s.i. has been found suitable.

The diffusion heating is preferably carried out for from two to four hours at a temperature between 350 and 450 C.; heating for four hours at 450 C. yielded the: best results.

In a number of cases where 0.00 thick silver layers had been applied to both the uranium and the jacket, the composition of the alloys formed was determined after completed bonding and heat treatment. The alloys formed were found to vary between 0.059 to 0.091 gram of mercury and from 0.418 to 0.560 gram of silver per inch of the final rod; the mercury content of the alloys varied firom 12.5 to 16.5%.

For silver coating the uranium cores, the following procedure was found advantageous:

The uranium core was first anodically cleaned in a solution containing six ounces per gallon of Anodex, which is an alkaline compound yielding a pH of 12 with ten ounces per gallon of water. bath was 180 F. and the current density was a.s.f.

Thereafter the core was rinsed with water and immersed for three minutes into a 35% solution of nitric acid at room temperature. removed from the uranium by rinsing it with hot water and then the core was anodically pickled in a bath containing 50% by weight of phosphoric acid and 20 cc. per liter of 37% hydrochloric acid with the bath at room temperature and a current density of 45 a.s.f. Thereafter the core was again rinsed with cold water and then immersed for five minutes in a 35 nitric acid solution. After another rinse with hot water, the core was ready for the silver coating. This was obtained by electrodeposition at 113 F. from a bath containing 75 g./l. of AgCN, 122 g./l. of KCN, and 22.5 g./l. of K CO the pH of this electrolyte had been adjusted to a value of 13 by means of KOH. The current density used was 25 a.s.f.; the time of electrolysis depended on the thickness desired of the silver layer.

The nickel jacket was prepared and coated in a similar manner. It was first cleaned with trichloroethylene and then brushed with a mixture of pumice and a solution of Nacconol, which is a wetting agent consisting essentially of the sodium salt of a sulfonated alkyl aromatic. Then the nickel jacket was anodically cleaned with Anodex of a concentration of six ounces per gallon of water; a current density of 75 a.s.f. was used for three minutes. Thereafter the nickel jacket was electropolished by applying a current density of 200 a.s.f. to a bath composed of 15% sulfuric acid, 63% phosphoric acid and 22% water, at a temperature of F. Thereafter the polished nickel jacket was treated in a bath containing 250 g./l. of NiSO .6H O and 50 g./l. of H 80 at room temperature with a current density of a.s.f., first anodically for ten seconds and then cathodically for one minute. The next 'b-ath used consisted of 7.5 g./l. of AgCN and 75 g./l. of KCN and was at room temperature; the jacket was immersed for two minutes while a current density of 5 a.s.f. was applied. Finally the silver coating proper was carried out using an electrolyte composed identically with that used for silver coating the uranium, also at 113 F., but using a current density of 15 a.s.f.

It will be understood that the above is merely one. possibility of carrying out the silver plating steps andv that other conventional ways may be used instead. How-- The temperature of the The excms of nitric acid was then at 700C. for 125 hours.

even-not all of the preparatory steps described are necessary, nor. is the silver plating per se being considered novel and part of the invention. The invention rather lies in the further bonding treatment ofthe'silver-coated members.

The hondsmade by the process of the invention show greatzdurability. Heating to temperatures up to 600 C. for about 150 hours in an argonatmosphere did not impair at all the bond obtained. Only a very slight degree ofdiffusion occurred, when the bonded article was heated temperatures of 100 C. and 550 C. as often as 60 times did not bring about any harmful effect on the quality of the bond.

Equally satisfactory results were obtained with jackets Likewise, cycling between I onto the assembly is used so as to reduce the area of said assembly'by from 5 to with regard to the actual metal present.

5. The process of claim 1 wherein the final homogenizing heating is carried out for from 2 to 4 hours at from 350 to 450 C.

6. The process of claim lwherein the final homogenizing heating is carried-out for about '4 hours at approximately 450 C.

7. A shaped articlecomprisinganranium core, a sheath therearound consisting of a material based on at least one metal selected from the group consisting of iron,

cobalt, nickel and alloys thereof, and an intermediate I metallic bonding layer consisting substantially of a silver consisting ofthe, metals setforth above but using indium as the alloying metal instead of mercury. I I

It will be understood that the invention is not intended to be limited to the details given in the specification, since modifications may be made -witl1in the scope of the appended claims.

I What is claimed is: I

1. A method of securely bonding to uranium a plate based on at least one metal selected from the group consisting of iron, cobalt, nickel and alloys thereof, comprising coating both the surfaces to be bonded with silver, alloying said silver coatings with a metal selected from the group consisting of mercury: and indium, assembling said plate and said uranium member, exerting pressure onto the assembly obtained, and. heating said assembly I whereby the bonding layers are homogenized.

2. The process of claim 1 wherein'the'silver coating is obtained by electrodeposition. 7

.3. The process of claim 1 wherein the silver coating is obtained by immersing into molten silver.

4. The process of claim 1 wherein-the pressure applied base metal.

8. The article of claim-7 wherein the sheath consists .of a nickel metal.

9. The article of claim 7 wherein the'sheath consists ofstainless steel.

.10. The article of claim 7- wherein the bond layer consists of a silver amalgam.

11. The article of claim 7 wherein the 'bond layer con- 'sists of a silver-indium alloy. 1 

7. A SHAPED ARTICLE COMPRISING A URANIUM CORE, A SHEATH THEREAROUND CONSISTING OF A MATERIAL BASED ON AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF IRON, COBALT, NICKEL AND ALLOYS THEREOF, AND AN INTERMEDIATE METALLIC BONDING LAYER CONSISTING SUBSTANTIALLY OF A SILVER BASE METAL. 